This disclosure relates to flow batteries for selectively storing and discharging electric energy.
Flow batteries, also known as redox flow batteries or redox flow cells, are designed to convert electrical energy into chemical energy that can be stored and later released when there is demand. As an example, a flow battery may be used with a renewable energy system, such as a wind-powered system, to store energy that exceeds consumer demand and later release that energy when there is greater demand.
A basic flow battery includes a redox flow cell having a negative electrode and a positive electrode separated by an ion-exchange membrane. A negative electrolyte is delivered to the negative electrode and a positive electrolyte is delivered to the positive electrode to drive an electrochemically reversible redox reaction. Upon charging, the electrical energy supplied causes a chemical reduction reaction in one electrolyte and an oxidation reaction in the other electrolyte. The ion-exchange membrane prevents the electrolytes from mixing but permits selected ions to pass through to complete the redox reactions. Upon discharge, the chemical energy contained in the electrolyte is released in the reverse reactions and electrical energy can be drawn from the electrodes.